Comet 30 vs Comet 40.

[Suffolk JK]

I just finished installing a 7HP Briggs into my Manco Red Fox, which has a Comet 30 clutch and 6" 30 series driven pulley. My buddy has an 8HP Briggs in his Manco Dingo with a Comet 40 clutch with a 7 1/2" driven pulley.

We were playing around yesterday since I was excited to see if I was going to be able to keep up since A) my cart is lighter and B) I'm 50 lbs. lighter than my friend...he blows my doors off at top speed and off the line by LOTS and LOTS of car lengths.

I've got half the size of tire on the rear and was very confused as to why it can't even keep up. Does it have to do with his Comet 40 and 7 1/2" driven pulley? Our axle and jackshaft sprocket are identical. I don't think 1HP would make THAT much of a difference.

My engine is running good. Carb is tuned to run perfect, it doesn't hesitate, new plug, has a return spring for the choke since it goes to half choke after a couple minutes of running. Throttle linkage does go 100% WOT. We even placed the governor spring a little on the loose side since it wasn't even revving to 3600 with the spring in the factory location. That made it feel 50 times better.

A little confused.

Thanks.

 

[Doc Sprocket]

While we still don't have ALL the information required to fully assess this, here are my thoughts: You say that he has 1hp more, 1 1/2" larger driven, much larger tires. You're lighter.

If your tires are significantly smaller, he will travel further per wheel revolution- think tire circumference

If messing with your governor got you more speed, odds are good that you were hitting 3600RPM, and now you're spinning faster still. If you were geared too high preventing max RPM, playing with the governor would have no effect. The only other possibility is that your governor is out of adjustment, and you were not hitting 3600. Hard to verify without a tach.

Under the right circumstances, 1hp can make a decent difference.

IIRC- the Comet 30 has a 3/4" belt and the 40 has a 7/8" belt. The 40 may hook up harder with less slip. The 30's engagement ratio is 2.68:1, the 40 (w/ 7" driven) is 2.43:1. Not a huge difference, but a little taller nonetheless. In the high range, your 30 gives you a .90:1 overdrive while the 40 tops out at 1:1. Your overdrive is nice, but see tire diameter comment.

As you can see, there is plenty of data to compare, even if all other things are equal, which they are not. For a full and proper evaluation, we would need measured tire diameters for both karts, actual sprocket tooth counts, more accurate kart descriptions and weights etc, including driver weights. We also have no idea what your max RPM really is, or his for that matter. Nor do we know if either CVT's drive or driven units are working properly and adjusted so. For all we know, your brakes or dragging or you have a half-frozen bearing. Maybe he modded his engine to spin 6000 RPM and isn't telling you. Too many possible factors.

At a glance, I can't help but hearken back to your governor adjustment comment. Unless your governor was out of whack to begin with, I think you were hitting 3600, and now you're spinning faster. Not necessarily a problem, but remember that his larger tire diameter equates to a higher road speed at the same wheel RPM. You may be geared a bit too low, you may not. Hard to tell without further detail. I don't think you're geared too high- if you were, futzing with the governor would do nothing for your top end.

I'm still wondering about the state of your engine, too- what's with the choke?

 

[r_chez_08]

What are the sprocket sizes, and the wheel diameter?
The comet 40 is overall more heavy duty, however the ratio is 2.43:1 to 1:1
I cannot find the ratio for the 30 series, however it cannot be much different.
I think it is probably the difference in wheel diameter.

 

[Suffolk JK]

I have about a 15" tall tire, took the measurement to the center and doubled it. I also have a 10-tooth jackshaft sprocket. His tires have to be at least 20-24" tall.

The choke question, it's a 1978 7HP Briggs with the updraft carb. I had to rig a spring from the choke lever to the air filter housing to keep it open when the engine runs. It's a little weak, so when the engine is running, with all the vibration, the choke starts closing to about 50%. The spring just holds it fully open after start up.

The only reason I think it wasn't revving to governer RPM is because it was definitely VERY quiet at "full" speed. His is fully governed as well without modification. So the spring was just placed at a different location at the governer arm so it won't fight to keep the RPMs soo low.

In terms of weight, his is a stock Manco Dingo and I'm on a stock Manco Red Fox. 250lbs him, 200lbs. me. Nothing has been modified.

Unless the previous owner of HIS cart did some engine work, I still can't see how he's fully accelerating off the line HARD and topping out WAY better than I am.

 

[Doc Sprocket]

Well, maybe a previous owner of your engine altered the governor setting to run slower- it is possible. It's also still possible that you are now above 3600. Again, without a tach it's all guesswork.

 

[jamyers]

I have about a 15" tall tire, took the measurement to the center and doubled it. I also have a 10-tooth jackshaft sprocket. His tires have to be at least 20-24" tall.
...

That's why he's outrunning you on the top end, his "legs" are longer.

Now, why he's getting the jump on you on the start, I don't know.